Sterilization method

ABSTRACT

A method of sterilizing a material, said method comprising the steps of: (a) introducing a solution comprising peroxyacetic acid into a hot gaseous stream to produce a peroxyacetic acid vapor; and (b) contacting such peroxyacetic acid vapor with the material to be sterilized.

FIELD OF THE INVENTION

The present invention is directed to a method of sterilizing a surfaceemploying a vapor comprising peroxyacetic acid. This vapor is created byintroducing a solution comprising diluted peroxyacetic acid solutioninto a hot gaseous stream. The use of such a true vapor results in thedesirable sterilization of a substrate without the deposition ofcondensate droplets onto its surface.

BACKGROUND OF THE INVENTION

The necessity of sterilizing surfaces for health and sanitary purposeshas long been recognized. Effective sterilization processes are neededfor a variety of purposes including aseptic packaging, medicalinstrument sterilization, biocidal vector environmental remediation,fumigation, vessel sterilization, food stuff treatments, and others.

Among the compounds known in the art which are useful for bacterialsterilization is peroxyacetic acid. Typically, peroxyacetic acid isemployed in aqueous-based systems as an equilibrium mixture comprisingperacetic acid, acetic acid, and hydrogen peroxide. While such systemshave been shown to be effective, in many instances a separate rinsingand/or drying step is required. This can add considerable expense andtime to the sterilization process, particularly when the substrate maybe adversely affected by high temperatures needed to expedite the dryingprocess.

It would therefore be highly desirable to possess a method for usingperoxyacetic acid as a sterilizing agent which method did not require anenergy intensive or time delaying drying step.

SUMMARY OF THE INVENTION

The present invention is directed to a method of sterilizing a material,said method comprising the steps of:

a) introducing a solution comprising peroxyacetic acid into a hotgaseous stream to produce a peroxyacetic acid vapor; and

b) contacting such peroxyacetic acid vapor with the material to besterilized.

This method permits the effective sterilization of a material withoutthe need for a subsequent drying step as solution droplets are notformed and not deposited upon the surface of the material so treated.Accordingly, a wide variety of materials may be rapidly and economicallysterilized employing the method of this invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a method of sterilizing a material,said method comprising the steps of:

a) introducing a solution comprising peroxyacetic acid into a hotgaseous stream to produce a peroxyacetic acid vapor; and

b) contacting such peroxyacetic acid vapor with the material to besterilized.

As is employed herein, the term vapor intended to mean a state in whichthe peroxyacetic acid is substantially entirely in the gaseous form.This is in contrast to mist or fog, both of which contain a significantproportion of liquid droplets suspended in the air. Unlike the use of amist or fog, it has been found the use of peroxyacetic acid in vaporform provides excellent sterilization of materials without theconcomitant formation of water droplets on the material surface.

Peroxyacetic acid is typically employed in the form of an aqueousequilibrium mixture of acetic acid, hydrogen peroxide and peroxyaceticacid. [ratios of 35:10:15]. Such composition may typically furthercomprise stabilizers such as phosphonic acids or phosphonates, i.e.Degquest 2010 or sequestriants such as dipicolinic acid, as well asother ingredients such as: mineral acid catalysts (sulfuric, nitric, orphosphoric acids); surfactants such as anionic laurylates, sorbitans andtheir respective esters, i.e. polyethylene sorbitan monolaurylates; andshort chain fatty esters (C6-C12) forming mixed peracids in solution.

Prior to introduction into the heated gas stream, the peroxyacetic acidis preferably diluted, by the addition of water, to a concentration ofless than about 10,000 ppm, preferably of less than about 4,000 ppm.

The heated gas stream is typically sterile air, although other gasessuch as nitrogen, CO₂, or inert noble gas carriers may also be employed.Such gas stream is typically heated to a temperature of at least about300° C., preferably to a minimal temperature of about 250° C. and can bein excess of 350° C. providing it can be cooled sufficiently forapplication. It then is typically cooled to between about 80° C. andabout 120° C. prior to the introduction of the peroxyacetic acidsolution. The heated gas stream at the point of peroxyacetic acid shouldhave a temperature of at least 5° C. higher than the dew point ofperoxyacetic acid (ca. 46.5°-49.9° C.); i.e., of at least about 55° C.,in order to ensure that the peroxyacetic acid is converted into a vaporrather than a fog or mist.

The peroxyacetic acid may be introduced into the heated air stream byany means well known to one of skill in the art. One preferred method isby direct injection of a solution.

The peroxyacetic acid vapor is then contacted with the material to besterilized for a period sufficient to kill the contaminants of concern.This time period will vary according to variables such as theconcentration of the peroxyacetic acid vapor employed; the nature of thesurface of the material to be sterilized; the particular contaminants tobe sterilized; the concentration of the contaminants to be sterilized;and the like. Typically, such contact will maintained for a period ofbetween about 15 and about 40 minutes.

A wide variety of materials may be sterilized employing the method ofthis invention, including hard surfaces of metals, plastics, polymers,and elastomers.

The present method may be used to sterilize materials contaminated withthose bacteria typically controlled by peroxyacetic acid in the liquidform. These include bacteria and spores of the genus Bacillus using B.thuringiensis and B. atrophaeus as surrogates for more pathogenicspecies (forms) such as C. botulinum as well as more typical genera ofbacteria, fungi, and viruses and protozoans often controlled by PAA suchas (but not limited to): Staphlococcus, Enterococcus, Salmonella,Capmylobacter, Pseudomonas, Candida, Rhizopus, Mucor, Influenza etc.

The following Example is presented to offer further illustration of themethod of this invention.

Example

Employing a DA 2000 aseptic pouch filler, 1.5 Liters of a dilutedsolution of peroxyacetic acid (having a concentration of 4000 PPM) wereinjected over a period of 17 minutes into a sterile air stream which hadbeen heated to 300° C. and allowed to cool to 90° C. No misting, fog orcondensate was observed, indicating that full vaporization had occurred.Coupons inoculated with the spore-forming organisms listed at theconcentrations listed were placed within the machine “head” sterileareas and exposed to the peroxyacetic acid vapor. No condensate wasobserved on any of the coupons tested. Upon completion of the injectionof the peroxyacetic acid solution, the coupons were immediately removedfrom the machine. Samples were taken from the coupons and transferred toappropriate growth media, cultured, and monitored for growth. Theresults of such testing are summarized in Table 1.

TABLE 1 Organism Total No Test # Organism Concentration Sites GrowthGrowth 1 B. thuringiensis 7.5 × 10⁴ 70 70 0 2 B. thuringiensis 7.5 × 10⁴70 70 0 3 B. thuringiensis 4.5 × 10⁵ 70 70 0 4 B. thuringiensis 4.5 ×10⁵ 70 69 1 5 B. thuringiensis 3.5 × 10⁶ 70 69 1 6 B. thuringiensis 3.5× 10⁶ 70 68 2 7 B. atrophaeus 3.1 × 10⁴ 9 9 0 8 B. atrophaeus 3.1 × 10⁴9 9 0 9 B. atrophaeus 2.0 × 10⁵ 9 9 0 10 B. atrophaeus 2.0 × 10⁵ 9 9 0

The above results demonstrate the excellent activity demonstrated by theperoxyacetic acid vapor employed in the method of this invention.

What is claimed is:
 1. A method of sterilizing a material, said methodcomprising the steps of: a) introducing a solution comprisingperoxyacetic acid into a hot gaseous stream to produce a peroxyaceticacid vapor; and b) contacting such peroxyacetic acid vapor with thematerial to be sterilized without the deposition of condensate dropletsonto the surface of such material.
 2. The method of claim 1 wherein suchmaterial is selected from the group consisting of metals, plastics,polymers and elastomers.
 3. The method of claim 1 wherein theperoxyacetic acid is diluted to a concentration of less than 10,000 ppmprior to being introduced into the hot gaseous stream.
 4. The method ofclaim 3 wherein the peroxyacetic acid is diluted to a concentration ofless than 4,000 ppm prior to being introduced into the hot gaseousstream.
 5. The method of claim 1 wherein the hot gaseous stream issterile air.
 6. The method of claim 1 wherein the hot gaseous stream isselected from the group consisting of nitrogen, carbon dioxide and noblegases.
 7. The method of claim 1 wherein the hot gaseous stream is heatedto a temperature above about 250° C. prior to the introduction of theperoxyacetic acid.
 8. The method of claim 1 wherein the hot gaseousstream is heated to a temperature above about 250° C. and is then cooledto a temperature of between about 80° C. and about 120° C. prior to theintroduction of the peroxyacetic acid.
 9. The method of claim 1 whereinthe temperature of the hot gaseous stream is at least about 5° C. higherthan the dew point of peroxyacetic acid.
 10. The method of claim 1wherein the contact between the peroxyacetic acid vapor and the materialto be sterilized is maintained for a period of between about 15 andabout 40 minutes.